Assemblies of this nature are widely used in the electrical industry, particularly in electrical cartridges which are mounted on a panel, either as individual units, or collectively as a keyboard of the same. Each cartridge is equipped with a cap which is slidably guided in the open end thereof to serve as the push-button actuator for a servomechanism which is mounted in the cartridge in advance of an operating unit, such as a switch unit, which is actuated thereby. The cap is usually illuminated to reveal intelligence thereon which is indicative of the nature or condition of the operating unit, and is preferably removable from the cartridge so that the illuminating lamps therein can be replaced when necessary. It is desirable, however, that the cap not be totally detachable from the cartridge, but instead be tethered to the same, so as to assure that it is not separated and lost when it is removed for the relamping operation. It is also desirable that the cap be securely latched to the servomechanism, when it is returned to the cartridge, so that forces acting on the cartridge during normal use and abuse of the same, such as shock forces, will not dislodge the cap and prevent it from being always readily available for the servo-function.
One object of the present invention, therefore, is to provide a mechanism whereby the cap can be releasably latched to the cartridge, when it is inserted therein, and the cartridge can be expected to withstand shock forces of limited duration and extent without the cap becoming dislodged therefrom, yet the latch mechanism can be overridden by a finger pull on the cap when it is necessary or desirable to remove it from the cartridge. Another object is to provide a latch mechanism of this nature whereby the cap can be latched to the servomechanism in the cartridge, and can become a part thereof for purposes of actuating the operating unit in the cartridge. A further object is to provide a latch mechanism of this nature which is adapted to function with any one of several servomechanisms, which may provide among them, for example, a momentary action effect, an alternate action effect, a latch and unlatch effect with respect to other cartridges in a keyboard of the same, or some other similar special effect which is suited to the operation of the unit inboard of the cartridge. A still further object is to provide a mounting base for the servomechanism whereby it can be readily interchanged with another such mechanism, notwithstanding that the same cap is retained and operably latched to the servomechanism as described. Still another object is to provide an intermediate actuator within the servomechanism, which is operable to actuate the operating unit while providing a degree of overtravel for the servomechanism otherwise. An additional object is to provide an electrical contact assembly, and a mounting technique for the same, whereby various electrical arrangements can be achieved in the cartridge, for purposes of illuminating the cap in such a way as to reveal different intelligence, or different combinations of intelligence on the cap. Still another object is to provide a mechanism whereby the cap is tethered to the cartridge, in the removed position thereof, yet can be released from the tether by a few simple steps that are readily executed with one's hands. Still further objects will become apparent from the description of the invention which follows hereafter.